Accurate and reliable determination of battery state of charge is essential to electric power management, fuel economy, and battery life. Battery state of charge is difficult to measure directly. One known method to measure battery state of charge is to infer the state of charge from the open circuit voltage. However, such known methods have accuracy shortfalls. Open circuit voltage-based state of charge estimation is influenced by battery hysteresis. Chemical processes internal to the battery create history dependant characteristics which influence battery performance. For any open circuit voltage, a range of states of charge may exist, depending on the conditions created by past charging and discharging cycles. Estimating the state of charge of a battery on the basis of open circuit voltage or similar electrical system properties would benefit from a method to evaluate and calculate the effects of historical charging and discharging cycles upon state of charge.